Spark plugs are used in conjunction with various types of combustion chamber configurations to initiate a flame in a flammable fuel and air mixture. Some combustion chamber configurations include passive pre-chamber, open chamber, and fuel fed pre-chamber configurations. Prior art spark plug designs suffer from various shortcomings, which can be amplified depending on the type of combustion chamber configuration in which the spark plug is operating.
As is known, spark plugs, in combination with pre-chambers and open chambers, are used to initiate combustion events within internal combustion engines. Pre-chamber are particularly useful for initiating and propagating the combustion flame for pre-mixed, lean-burn natural gas engines which can be difficult to ignite using conventional open chamber type configurations. Passive pre-chambers include a combustion volume in which the spark plug is located. The combustion volume of the pre-chamber is linked to the main combustion chamber by the use of orifices or nozzles. The spark plugs tend to include a central cathode electrode and one or more outer ground or anode electrodes, which at least partially surround the cathode electrode to create a gap therebetween. The spark plug initiates a combustion event by generating a spark (e.g., electron current) that spans the gap between the central and outer electrodes. More specifically, the spark initiates a flame that propagates through the pre-chamber volume. This combustion creates a sudden increase in pressure in the pre-chamber creating a large pressure difference across the orifices between the pre-chamber and main chamber. The pressure difference forces the flame to propel through the orifices into the main combustion chamber resulting in a successful combustion event.
After a successful combustion event, the residual exhaust gases in the main chamber are scavenged during the exhaust stroke. During the intake stroke, a fresh, pre-mixed air and fuel mixture (charge) is pushed into the main cylinder via a compression event driven by a piston. Some residual exhaust gases in the passive pre-chamber volume and between the spark plug electrodes, however, are not completely scavenged and remain within the pre-chamber during the exhaust and intake strokes. During the subsequent compression stroke, the pressure difference between the main chamber and pre-chamber increases forcing a fresh charge through the orifices into the pre-chamber, which compresses the residual exhaust gases towards the backside of the pre-chamber where the spark plug is located.